With the advent of integrated circuits, electronic devices of this type have been encapsulated in various plastic materials to form low cost, easily handled packages. Since these plastic encapsulants are not moisture resistant, moisture related failures are the primary problems encountered in utilizing plastic-packaged devices. Extensive T-H (temperature-humidity) testing is commonly used in order to minimize these types of problems.
In the past, these devices have been tested, some by pressure cooker heating and some by separate 85/85 (85.degree. C. and 85% relative humidity) testing. These two separate procedures have been the standard techniques for the evaluation of plastic-packaged semiconductor devices, primarily because these methods are simple, reliable and relatively reproducible. The primary failure mechanisms in pressure cooker testing are chemical corrosion and threshold shifts, while the primary failure mechanism in 85/85 testing is electrolytic corrosion. Improvements in both device processing and passivation, and plastic encapsulants and molding techniques have significantly improved the reliability of plastic-packaged devices, and, therefore, longer 85/85 testing time of 1000-2000 hours are often required. For this reason, there have been several efforts to develop more accelerated testing techniques in order to decrease what has developed into excessive 85/85 test times. However, none of these is completely satisfactory.
The present invention provides an optimum method of accelerating the testing of plastic-encapsulated devices by increasing the moisture ingression rate by means of a sequential procedure that utilizes pressure cooker conditions to rapidly drive the moisture to the die surface, followed by 85/85 to produce electrolytic corrosion. This technique is entitled Pressure Cooker and Temperature Humidity or PCTH processing.